• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.9
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• pp.829-840
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• 2012

Recently, in network communication environments, it is changing very fast from wired to wireless. The open shortest path firtst (OSPF), one of link state routing protocols, mainly used in wired networks, is the routing method to select optimal traffic path as identifying the link state of neighbor routers. The traditional OSPF cost functions performs with first fixed cost permanently, unless the router link is changed. However, in wireless networks, the performance of links show big difference by other environment factors. The bit error rate (BER), a parameter which can quite affect link state in wireless networks, is not considered in the traditional OSPF cost functions. Only a link bandwidth is considered in the traditional OSPF cost functions. In this paper, we verify the various parameters which can affect link performance, whether it is permissible to use as the parameter of proposed cost functions. To propose new cost functions, we use the effective bandwidth. This bandwidth is calculated by proposed formula using the BER of the network link and link bandwidth. As applied by the proposed triggering condition, the calculated effective bandwidth decrease the unstable of network by generating less link state update messages in wireless networks that frequently changes the link state. Simulation results show that the proposed cost functions significantly outperforms the traditional cost functions in wireless networks in terms of the services of VoIP and data transmission.

• Proceedings of the KOR-KST Conference
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• 2007.05a
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• pp.89-97
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• 2007

본 연구에서는 통행배정 모형이 갖는 여러 가지 가정 중 대칭적 통행비용 함수를 갖는 가정을 극복할 수 있는 방법에 대해 살펴보았다. 통행배정 문제에 있어서 대칭적 비용함수 가정이라는 것은 링크의 통행비용은 다른 링크의 교통량에 전혀 영향을 받지 않는 않으면서, 동시에 해당 링크를 통과하는 단하나의 수단에 의해서만 결정된다는 의미이다. 본 연구에서는 이러한 가정을 극복할 수 있는 비대칭 통행배정모형의 특성을 살펴보고, 그 해석 모형에 대해 고찰하였다. 이 때 대표적 비대칭 통행배정 문제인 다수단 통행배정 모형을 중심으로 문제를 정의하여 검토하였다. 대각화(Diagonalized) 알고리즘과 Column Generation에 기반한 heuristic 모형을 다수단 통행배정 모형에 적용하여 그 결과를 분석하였다. 그 과정을 통해 대각화 알고리즘은 초기해의 수단과 수렴기준 수단에 따라 서로다른 해를 갖는 복수의 평형해(Equilibria)특성을 가지고 있었다. 그에 비해 Column Generation에 기반한 heuristic 모형은 Euclidean Norm을 이용한 부분최적화를 통해 복수의 평형해(Equilibria)에 관한 문제점을 개선할 수 있었다.

• Journal of Korean Society of Transportation
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• v.26 no.1
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• pp.103-112
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• 2008

In the feasibility analysis, Braess' Paradox results in the negative social benefit in spite of adding transportation facilities. Consequently, it has been difficult to judge on the investment of SOC projects. This research aims to analyze the Braess' Paradox in the feasibility analysis and to seek a remedy for the Paradox. Several experiments were conducted on the simple network under the various conditions. From the experiments, following findings were validated: Braess' Paradox occurred only if travel demands met within certain intermediate range. In terms of traffic assignment method, the SO was more likely to reduce the effect of the Braess' Paradox than the UE. However, the Braess' Paradox in the benefit of operating cost saving occurred in all cases and the paradox in the total benefit continued. In order to solve the problem, new link cost function considered travel time and operating cost simultaneously were suggested. As a result, the negative benefit was significantly decreased in the UE case and total negative benefit was no longer shown in the SO case through the analysis.

• Journal of Korean Society of Transportation
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• v.25 no.6
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• pp.161-170
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• 2007

The purpose of this study is to find the solution that overcomes the existing assumption of symmetric cost functions in multi-class assignment. In the assignment problem, the assumption of a symmetric cost function means that the link cost is determined by each unique mode and is not affected by any other modes. In this study, the authors have applied a diagonalized algorithm and a heuristic model based on column generation to a multi-class assignment model and analyzed the result. Through the study, the authors found that the diagonalized algorithm produces equilibrium solutions by the initial convergence condition. In contrast to the diagonalized algorithm, the column generation algorithm has improved the solution model to overcome the problem of equilibrium solutions in the diagonalized algorithm.

• Proceedings of the KOR-KST Conference
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• 1998.10a
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• pp.31-40
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• 1998

본 연구의 목적은 기존의 Cell Transmission(1994, Daganzo) 교통류 이론을 기반으로 동적통행배정 모형을 개발하는 것이다. 이 모형은 동적 O-D 발생모듈, HOV 차선모듈, 분류부 분할모델, 링크비용함수 모듈, 최단경로 탐색 모듈등으로 구성된다. 이 모델에서 적용하는 교통류 모델은 각 링크를 동일한 특성을 가지는 셀로 구분하여 셀내의 진입시간과 진출시간을 계산하여 링크비용을 계산하는데 이것은 비용의 과대·과소 추정을 피할 수 있으며 교통지체 현상을 현실적으로 표현해 줄 수 있는 장점이 있다. 또한 HOV 차선 모듈에 의해 수단별 교통류 진행 및 비용고려가 가능하며 HOV 차선의 평가 및 분석이 가능하다. 기존의 동적통행배정모형은 매 시간대별 출발지에서 균형상태를 추구하는 통행배정기법을 사용하고 있지만 이 모델은 분류되는 노드를 가상의 출발점이라고 가정하여 각 시간대별로 최단경로를 탐색하여 균형상태를 추구해나가는 기법을 적용하고 있다. 각 셀별 차량을 목적지별, 차종별, 대기시간별로 추적하여 진행시키며 분류부에서는 최단경로를 탐색하여 배분된다. 또한 진행하고자 하는 셀의 용량과 현재 셀의 밀도를 고려함으로서 용량제약 하에서의 동적통행배정모형을 적용하고 있다. 이 모형은 고속로의 합류부 및 분류부의 교통특성을 세밀히 분석할 수 있으며, TCS 및 램프미터링과 접목하여 고속도로 운영에 이용될 수 있으며, 고속도로 중·장기적인 계획에 이용될 수 있다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.23 no.2
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• pp.1-14
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• 2024

The most optimal route-search algorithm thus far has introduced a method of applying node labels and link labels. Node labels consider two nodes simultaneously in the optimal route-search process, while link labels consider two links simultaneously. This study proposes a turn-label-based optimal route-search technique that considers two turns simultaneously in the process. Turn-label-based optimal route search guarantees the optimal solution of dynamic programming based on Bellman's principle as it considers a two-turn search process. Turn-label-based optimal route search can accommodate the advantages of applying link labels because the concept of approaching the limit of link labels is applied equally. Therefore, it is possible to reflect rational cyclic traffic where nodes allow multiple visits without expanding the network, while links do not allow visits. In particular, it reflects the additional cost structure that appears in two consecutive turns, making it possible to express the structure of the travel-cost function more flexibly. A case study was conducted on the metropolitan urban railway network consisting of transportation card terminal readers, aiming to examine the scalability of the research by introducing parameters that reflect psychological resistance in travel with continuous pedestrian transfers into turn label optimal path search. Simulation results showed that it is possible to avoid conservative transfers even if the travel time and distance increase as the psychological resistance value for continuous turns increases, confirming the need to reflect the cost structure of turn labels. Nevertheless, further research is needed to secure diversity in the travel-cost functions of road and public-transportation networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12B
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• pp.1211-1218
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• 2010

OSPF is the optimized routing protocol in wired network and considered as a tactical routing protocol in wireless tactical communication network. However because it is designed basically based on wired environment, it runs inadequately in wireless tactical environment: noise and jamming signal. So, we proposed new OSPF cost function to develop active routing protocol in wireless tactical communication network. In redefined cost function, there are four parameters that are relative transmission speed, link weight, router utilization, link average BER(Bit Error Rate). These parameters reflect wireless tactical characters. Also, we remodel the option field in Hello packet. It can help user to periodically check the link state. From the simulation result, it is shown that proposed OSPF is better than OSPF in jamming situation and has accumulative delay gain with dispersion of traffic load in entire network.

• Journal of Korean Society of Transportation
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• v.23 no.2
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• pp.117-130
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• 2005

In both deteministic user Optimal Traffic Assignment Model (UOTAM) and stochastic UOTAM, travel time, which is a major ccriterion for traffic loading over transportation network, is defined by the sum of link travel time and turn delay at intersections. In this assignment method, drivers actual route perception processes and choice behaviors, which can become main explanatory factors, are not sufficiently considered: therefore may result in biased traffic loading. Even though there have been some efforts in Stochastic UOTAM for reflecting drivers' route perception cost by assuming cumulative distribution function of link travel time, it has not been fundamental fruitions, but some trials based on the unreasonable assumptions of Probit model of truncated travel time distribution function and Logit model of independency of inter-link congestion. The critical reason why deterministic UOTAM have not been able to reflect route perception cost is that the route perception cost has each different value according to each origin, destination, and path connection the origin and destination. Therefore in order to find the optimum route between OD pair, route enumeration problem that all routes connecting an OD pair must be compared is encountered, and it is the critical reason causing computational failure because uncountable number of path may be enumerated as the scale of transportation network become bigger. The purpose of this study is to propose a method to enable UOTAM to reflect route perception cost without route enumeration between an O-D pair. For this purpose, this study defines a link as a least definition of path. Thus since each link can be treated as a path, in two links searching process of the link label based optimum path algorithm, the route enumeration between OD pair can be reduced the scale of finding optimum path to all links. The computational burden of this method is no more than link label based optimum path algorithm. Each different perception cost is embedded as a quantitative value generated by comparing the sub-path from the origin to the searching link and the searched link.

• Journal of Korean Society of Transportation
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• v.28 no.1
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• pp.115-124
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• 2010

VDF(volume-delay function) is one of the most important factor to improve the reliability of traffic demand estimation because it is for estimation of link travel time based on the traffic volume variation. Because VDF of link except for freeway is applied as the parameter of BPR(bureau of public road) of U.S., it causes to deteriorate the accuracy of traffic demand estimation. The purpose of this paper is to establish new parameter of VDF based on the real-surveyed traffic data in order to improve the problem of the existing VDF. We suggest the reclassification of road hierarchy, the approach of traffic survey, the estimating method of VDF parameter, and the improvements of new VDF application. The new VDF allows us to estimate more realistic traffic situation in parts of demand, travel time and path between origin-destination.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.4
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• pp.370-379
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• 2014

Recently, the interest in optical network with multifiber link is continuing to rise since the network traffic has been growing exponentially. However, growing traffic in network leads to increasing the energy consumption of the network equipment. In this paper, we propose a dynamic routing and wavelength assignment (RWA) algorithm based on V-like cost function and layered graph to improve energy efficiency in IP over WDM network with multifiber link. The V-like cost function is used to decide the fiber cost according to the number of used wavelengths. The layered graph with multifiber link is used to select the energy efficient route and wavelength. The proposed RWA algorithm is compared and analyzed with conventional algorithm in view of average power consumption and blocking probability through OPNET modeler.